The present invention relates to components that operate at high temperatures, such as turbine airfoil components of turbomachinery. More particularly, this invention relates to an airfoil component equipped with one or more internal cooling passages connected to one or more internal cooling chambers capable of promoting the heat transfer characteristics within the component.
Components of turbomachinery, such as buckets (blades), nozzles (vanes), and other hot gas path components of industrial and aircraft gas turbine engines, are typically formed of nickel, cobalt or iron-base superalloys with desirable mechanical and environmental properties for turbine operating temperatures and conditions. Because the efficiency of a turbomachine is dependent on its operating temperatures, there is a demand for components, and particularly airfoil components such as turbine buckets and nozzles, to be capable of withstanding increasingly higher temperatures. As the maximum local temperature of a superalloy component approaches the melting temperature of the superalloy, forced cooling with a suitable fluid, typically air, becomes necessary. For this reason, airfoils of gas turbine buckets and nozzles often require complex cooling schemes in which a cooling fluid, typically compressor bleed air, is forced through internal cooling passages within the airfoil and then discharged through cooling holes at the airfoil surface to transfer heat from the component. Convection cooling occurs within the airfoil from heat transfer to the cooling fluid as it flows through the cooling passages. In a technique referred to as impingement cooling, additional cooling can be achieved with fine internal orifices that direct cooling fluid directly against the inner surfaces of the outer walls of the airfoil. Cooling holes can also be configured so that cooling fluid is released into the gas path at specific locations on the component surface to provide a layer of cooling fluid flow over the component surface, creating a boundary layer (film) that reduces heat transfer from the hot gas path to the component.
Considerable cooling fluid is often required to sufficiently lower the surface temperature of an airfoil component. To promote heat transfer efficiency from the airfoil to the cooling fluid, it may be desirable or necessary to provide internal features in the internal surfaces of the cooling circuit. Such features have included ribs, turbulence promoters, crossover holes, trail edge slots, serpentine passages, etc. The inclusion of metallic foam or similar porous and permeable materials has also been proposed to promote heat transfer within airfoil components. For example, U.S. Published Patent Application Nos. 2006/0021730, 2007/0274854, 2008/0250641, 2009/0081048, 2010/0239409 and 2010/0239412 propose the use of a metallic foam or similar material to fill the interior and/or cooling holes of an airfoil, such that the airflow through the foam is largely unidirectional.